Should I have killed Iosefka?

I haven’t fully explored forbidden woods yet, I found the path to the clinic and killed Iosefka. She was already aggro so I assumed she was someone I had to kill. I didn’t get anything besides the communion so I thought I messed up and killed an NPC.

I looked it up and some people are saying that if you kill Iosefka you lock yourself into an ending which isn’t the “true” ending. Is this true? Will it matter too much in the long run?

Try not to spoil too much please